The present invention relates to monolithic capacitor arrays. Such arrays may be used, for sample, for suppression of electromagnetic interference (EMI).
It is frequently necessary to suppress EMI (or “noise”) in both electronic signal lines and power lines and it is well known to achieve this using capacitive filter circuits, particularly LC circuits.
In applications requiring filtering of several lines, a set of capacitors may be arranged in an array. GB 220520 teaches how such an array can be incorporated in a volumetrically efficient way, in a multi-way connector. Further, the capacitors may be formed in a common, monolithic ceramic body as in the known arrangement illustrated in FIG. 1, wherein the ceramic body is designated by reference numeral 1 and has a plurality of metallised bores 2 through which pass respective connector pins 3. The equivalent filter circuit, for each of the connector pins 3, is illustrated in FIG. 4 and comprises an inductance 50 connected at both ends to the signal line 52 (formed by the connector pin 3) and also through first and second capacitors 54, 56 to ground. Looking again at FIG. 1, first capacitor 54 comprises pin-side plates 5, connected to an upper region of the pin 3 through the metallisation of the hole 2 and interleaved with ground-side plates 7 to be connected through metallisation 9 at the array's outer face, to ground. Similarly second capacitor 56 comprises pin-side plates 11 connected to a lower region of the pin 3 through the metallisation of the hole 2, interleaved with ground-side plates 13 to be connected through the metallisation 9 to ground. The required inductance is provided by virtue of a ferric inductor “core” 15 disposed around the pin 3 in the hole 2.
Constructional difficulties arise because the metallisation of the holes 2 through which the pins 3 pass must be in two isolated sections: an upper part for connection to plates 5 of the first capacitor and a lower part for connection to plates 11 of the second capacitor. Contacting these metallisation to the pins 3 is also problematic and the construction constrains the dimensions of the ferrite.